1. Field of the Invention
The present invention relates to a method of adaptive quantization in differential pulse code modulation and a system for transmitting quantized data.
2. Description of the Prior Art
The 8-mm video tape recorder, for example, has an optional function for digitizing an audio signal in accordance with PCM (pulse code modulation) as a PCM signal, and recording the same in an overscan interval during recording, and reproducing the original audio signal by the opposite processing thereof during playback or reproduction.
In this event, the audio signal can be recorded and/or reproduced with better characteristics when the sampling frequency, and the quantizing bit length of the PCM signal, are increased. However, such increase in the sampling frequency and the quantizing bit length greatly increases the number of bits to be recorded and/or reproduced, thereby making it impossible to record and/or reproduce the audio signal.
Thus, it has been proposed to compress the bit number of PCM signals upon recording, and expand the bit number upon reproduction, such that excellent recording and/or reproducing characteristics can be obtained even with a fewer number of signal bits recorded on a tape.
One such bit compress and expansion method is a so-called ADPCM system (See "Fundamental Audio Information processing" published by Ohm Co. and Japanese Patent Application No. 61-299285).